Stream correct

streamcorrect.scala

val route = path("download") {
    get {
      optionalHeaderValueByName("Range") {
        case None =>
          // there must always be range header
          complete(StatusCodes.RequestedRangeNotSatisfiable)

        case Some(range) =>
          val file = new File("movie.mp4")
          val fileSize = file.length()
          //Range header is usually Range: bytes=12943360-
          val rng = range.split("=")(1).split("-")
          val start = rng(0).toInt

          //most of the time, there is no end range, just a start, in that case,
          //we use the file size as the end range.
          val end = if (rng.length > 1) {
            //there is end range
            rng(1).toLong
          } else {
            fileSize - 1
          }
          respondWithHeaders(List(
            RawHeader("Content-Range", s"bytes ${start}-${end}/${fileSize}"),
            RawHeader("Accept-Ranges", s"bytes")
          )) {
            complete(HttpResponse(StatusCodes.PartialContent, entity = HttpEntity(MediaTypes.`video/mp4`,
              FileIO.fromPath(file.toPath, 8192, start.toInt))))
          }
      }
    }
  }